The studies in endocrinology and cell biology have provided a general understanding of the peptide hormone biosynthetic, posttranslational processing and secretion from a number of different endocrine cell types. More recent molecular approaches have greatly augmented that knowledge by defining the integral components of the different subcellular compartments and delineating the mechanisms that regulate intracellular transport and trafficking along the secretory pathway. The three specific aims of this renewal application are: 1) to determine the nature and sites where trimeric G protein Galphai3, affects intracellular transport along the AtT-20 corticotrope secretory pathway; 2) to gain insight into Galphai3's intracellular signaling pathway in pituitary cells by identifying molecules that interact with Galphai3 using the yeast two-hybrid system; and 3) to determine the relationship between rough ER, SEREC (smooth ER exit compartment) and ERGIC (ER-Golgi intermediate compartment) in AtT-20 cells. Fundamental information derived from these studies should provide new information on the molecular mechanisms of hormone secretion in neuroendocrine cells.